This invention relates to a technology for preventing a cracked bottom of an extrusion-blow molded container having a cylindrical body.
There is proposed an extrusion-blow molded container, particularly a delaminatable blow-molded container having an air inlet hole arranged at a neck of the container. In order to prevent a bottom from cracking, such container is formed with a bottom rib in a bottom seal section. The bottom seal section includes fusion-bonded sections, each of which is provided with projections to be inserted into the other member for mutual engagement of the fusion-bonded sections (Japanese Patent Laid-Open No. 8-216238).
In the above described prior art, the bottom rib is formed in the bottom seal section of the blow-molded container by fusion-bonding a pair of fusion-bonded sections projecting from a bottom wall of the container at inner surfaces thereof. The fusion-bonded sections of the bottom rib are provided with projections and recesses alternately, so that the fusion-bonded sections may be held in mutual engagement with each other, so as to make the bottom seal section show an improved cohesive force and an enhanced strength against shearing force that can be applied in parallel with a parting line (along X-X' line in FIG. 2). With such an arrangement, the crack of the bottom of the extrusion-blow molded container having large volume is prevented.
Particularly, in the case of a delaminatable blow-molded container, such projections and recesses are very advantageous, because inner layers of the container that are typically made of a poorly adhesive resin material such as nylon can be tightly bound together due to the projections and recesses, and hence the bottom of the container is practically free from cracking.
However, containers having an elliptic cylindrical body and an elliptic bottom (hereinafter referred to as "elliptic cylindrical containers") and those having a column-shaped body and a circular bottom (hereinafter referred to as "cylindrical containers") differ significantly from each other in terms of the phenomenon of cracked bottom. In the case of the delaminatable blow-molded container having the inner layers typically made of a poorly adhesive resin material, the bottom can easily become cracked when the container is filled with liquid or accidentally dropped, if the container is a not an elliptic container but a large cylindrical container.